The present invention relates generally to laser-based pipe alignment systems which use a reference beam of light along a predetermined path to position sections of pipe and, more particularly, to a pipe alignment system and method wherein a reference beam of light in the green portion of the optical spectrum is aligned with an optical target inserted in a section of pipe as the position of the pipe is adjusted.
Systems employing a reference beam of laser light have been used in numerous surveying and construction applications. In particular, such systems have been advantageously used to lay sections of pipe. Typically, a laser beam transmitter provides a reference laser beam which is transmitted through the previously positioned pipe sections along a central axis. A laser beam target having reference indicia thereon is placed within a section of pipe to assist workers in positioning the pipe.
One such laser beam target is disclosed in commonly assigned, U.S. Pat. No. 5,095,629, the disclosure of which is hereby incorporated by reference. The end of the pipe opposite the laser beam target is aligned with the end of a previously laid pipe section. The newly laid pipe section is then maneuvered until the reference beam of light strikes the reference indicia on the target. Support material, such as gravel, is placed under the pipe section to support and hold the pipe section in place.
These prior pipe alignment systems have primarily employed gas or semiconductor lasers which emit light in the red portion of the light spectrum (approximately 630-700 nm). Consequently, laser beam targets have hitherto been designed for optimum detection of incident light in the red portion of the optical spectrum. A worker can then view an image of the light beam where it strikes the target and align this image with the reference indicia on the target.
Prior pipe alignment systems have experienced various problems associated with the use of light in the red portion of the optical spectrum. High power levels are needed to emit a red light beam with sufficient brightness to properly operate the system and be readily apparent to the human eye. Power levels which are too high can be hazardous to operators of the system. As is well known, various eye injuries can result from prolonged exposure to high powered laser beams. In view of the potential health hazards, federal and international regulatory and enforcement agencies have strictly regulated the construction and use of lasers. These regulations, although extremely beneficial to the health of laser users, severely restrict the maximum power of lasers which may be employed in pipe alignment systems. This, in turn, has limited the useful operating ranges of prior art alignment systems.
In addition, it has been found that the use of a red light beam restricts the useful range of pipe alignment systems. During propagation of a light beam, the diameter of the beam enlarges in proportion to both distance and wavelength due to inherent diffraction. Since red light has the longest wavelength of any visible light, it necessarily experiences a large amount of diffraction divergence over distance. Consequently, the alignment accuracy of a pipe alignment system using a red beam of light is limited by this enlargement of the light beam.
For the foregoing reasons, there is a need for a pipe alignment system and method utilizing a low powered light source which is operable over greater distances, and in which diffraction divergence is reduced to allow more accurate alignment of sections of pipe.